[Ed. note: Botany Blueprint will be a regular column about the form and function of seed cases, intended to advance botanic literacy and make plants relevant to a broad audience. The project will cover 100 specimens in total, and it will detail the design of the seed case and its function in the plant's life cycle. Some are particularly fascinating, from a design perspective, through sheer precision and simple beauty. This is the first entry in this project.]
Specimen #1: Jacaranda mimosifolia
n warm climates the world over, seasons are marked by the flowering of the jacaranda tree. An Australian holiday song reminds its carolers, “When the bloom of the jacaranda tree is here, Christmas time is near.” In South Africa, the flowers ominously signify university year-end exams. And in Los Angeles, it’s car wash season: the ubiquitous tree liberally sheds its lavender blossoms—with sticky residue—on objects below. The jacaranda is thus best known for its hazy purple canopy, but here we’ll examine what comes next: its fruit, or seed cases. Flowers yield seeds, and seeds yield more trees.
And so, by the time lavender blossoms carpet the ground, the tree has begun to sketch its next project: the fruit. An apple tree yields apples, a lemon tree, lemons. Other trees, however, like the jacaranda, haven’t designed their fruit for human consumption. Their fruit, or seed cases, are engineered to discourage unwanted attention from hungry foragers. The jacaranda’s seed cases are impenetrable: hard, thick disks that resemble castanets or tapered hockey pucks. Too high to be plucked, too woody to be eaten, the capsule’s architectural directives are physics and timing. Its design strategy is in some ways self-reliant, but with one necessary agent: the wind.
A jacaranda relies on air currents to disseminate its seeds, which are encased in a papery wing that carries them away in a passing breeze. But timing is critical. The development process is predicated on an overarching principle: keep the final product under wraps until it’s viable. A fruit’s purpose is to produce seeds (a function the plant spends no shortage of energy ensuring), but a seed that’s not ready to grow isn’t much use to the tree. And so the seams are stubbornly sealed until the seeds are mature. When the fibrous aerodynamic engineering is complete and the tiny passengers are poised to germinate, the capsules split open to submit their seeds to the wind. Meanwhile, the jacaranda clings tightly to the cases: hinged agape, seeds fluttering away in the breeze.
Botany Blueprint #2: The Wild Cucumber